NO164697B - SURGICAL OSTEOS SYNTHESIS OR COMPONENT OF SUCH THEM, AND PROCEDURES FOR PREPARING IT. - Google Patents

Abstract

Surgical osteosynthesis composite material, which is self-reinforced i.e. it is formed about the absorbable polymer or copolymer matrix which is reinforced with the absorbable reinforcement units which have the same chemical element percentage composition as the matrix has.

Description

This invention relates to a surgical osteosynthesizing agent or component of an osteosynthesizing agent with a composite structure such as a plate, a rod, a marrow nail or the like made of polymer or copolymer which is observable under tissue conditions.

The production of osteosynthesis materials from absorbable polymers is known from several patents. The manufacture of absorbable structures and surgical elements from polyglycolide (PGA).

has been described in US Patent No. 3,297,033 and US Patent No. 3,739,773.

Sutures made from polylactide (PLA)

is described in US patent no. 2,703,316.

Sutures made from glycolide/lactide copolymers (PGA/PLA)

(where n and m are integers > 1) is described in US patent no. 3,839,297. Sutures and osteosynthesis devices made from poly-g-hydroxybutyric acid (PHB)

is described in British Patent No. 1,034,123.

Sutures and osteosynthesis devices made from polydioxanone (PDS)

is described in US patent no. 4,052,988.

Absorbable surgical devices made from polyester amides (PEA)

is described in US patent no. 4,343,931.

Absorbable surgical sutures and surgical devices constructed from copolymers containing units of structural formula (VII)

as end sequences and the units of formula (VII) randomly combined with the units (VIII)

as middle sequences are described in Finnish patent application 83.2405.

Absorbable surgical devices in the above-mentioned inventions are often plates that are attached to bones with screws, cylindrical medical nails or similar structures that are produced by melting absorbable polymer and by molding or pressing the melt into the appropriate shape. The mechanical strengths of such samples produced by melt processing techniques are often of the same order of magnitude as those from other similar synthetic polymers. Accordingly, the tensile strength of dry, non-hydrolyzed samples prepared from PBA, PLA, PHB and PGA/PLA is often in the order of 40-80 MPa (see, e.g., Kulkarni, R.K, Moore, E.G., Hegyeli, A.F. and Fred, L., J. Biomed. Mater. Res., 1971, 5, 169, Vert, M., Chabot, F. and Leray, J., Makromol. Chem., Suppl., 1981, 5, 30, Christel, P., Chabot , F., Leray, J.L., Morin, C. and Vert, M., in Biomaterials (Eds. G.D. Winter, D.F.Gibbons and H. Plenk, Jr.), Wiley (1980), p. 271, Tune, D.C., Transactions of 9th Annual Meeting of the Society for Biomaterials, Birmingham, U.S.A., 1983, p. 47, Howells, E.R. Chem.Ind., 1982, 7.509)

The tensile strength given above is moderate compared to the tensile strengths of compact bone (approx. 80-200 MPa).

In addition, melt-treated homogeneous polymer samples of the above-mentioned polymers are in several cases brittle or too flexible to be used for bone surgery purposes. Therefore, the common use of resorbable polymers in bone surgery has encountered serious difficulties.

The initial mechanical strength of surgical absorbable osteosynthesis materials has been improved by using in absorbable polymeric matrices absorbable fibers with a higher melting point than the matrix itself as reinforcement units (e.g. polylactide matrix reinforced with polyglycolide fibers in US patent no. 4,279,249). Biostable carbon fibers have also been used as reinforcement units. When the chemical structure or elemental composition of the reinforcement units differs from that of the matrix material, the materials usually cannot form strong chemical primary or secondary bonds between each other, which leads to poor attachment between the material components.

Adhesion promoters, such as silanes or titanates, etc., which are normally used in polymeric reinforcing compositions,

cannot be used in surgical materials intended for use in surgery due to their toxicity. Therefore, it is difficult to achieve good adhesion between matrix and reinforcement units of different chemical origin.

The invention is essentially characterized in that the osteosynthesis material or the component of the osteosynthesis material has a self-reinforced structure, i.e. it consists of at least one matrix, which consists of absorbent polymer or copolymer and has as reinforcement absorbent fibers with a similar chemical structure. It should also be noted that the matrix and reinforcement units having the same chemical element-percentage composition may also be isomers, meaning that the matrix and reinforcement units have configurations that differ from each other.

The invention relates to self-reinforced absorbable polymers.

surgical osteosynthesis materials which have a uniform chemical element structure and which therefore have good adhesion between matrix and reinforcement elements. Therefore, the material has excellent initial mechanical strength properties such as high tensile strength, bending and shear strength and toughness, and therefore this material can be successfully used in surgically absorbable osteosynthesis devices or as components or parts of such devices such as osteosynthesis plates attached to bone with screws, as fastening screws, as core nails or as components (plates, rods or rods) of such osteosynthesis devices as are described in Finnish patent 61402.

Self-reinforcement means that the polymer matrix is reinforced with the reinforcing units (such as fibers) that have the same chemical percentage element composition as the matrix. By applying the self-reinforcing principle, the high tensile strength (preferably 500-900 MPa) of fibers can be used effectively in the production of macroscopic samples. When strongly oriented fiber structures are bonded together with the polymer matrix which has the same chemical element composition as the fibers, the composite structure is obtained which has excellent adhesion between matrix and reinforcement units and therefore also excellent mechanical properties.

The attached drawing schematically shows the structure of the material in this invention where the absorbable polymeric matrix is reinforced with the absorbable fibres.

The method is mainly characterized by the part of the material that will form the matrix being exposed to heat and/or pressure in such a way that the physical state of the part of the material that will act as the matrix phase enables the development of adhesion between the nearby reinforcement units and the matrix.

There are alternative methods that can be used in the production of self-reinforced absorbable osteosynthesis materials in this invention. One method is to mix finely ground polymer powder with fibres, threads or equivalent reinforcement units produced from the same material or from its isomer with the same chemical percentage element composition and heat the mixture under such conditions and using such temperatures that the finely ground particles soften or melt , but the reinforcement unit structures do not soften or melt significantly. When such a mixture is pressed into the correct shape, the softened or melted particles form the matrix phase that binds the reinforcement unit together, and when this structure cools, a self-reinforced mixture with excellent adhesion and mechanical properties is obtained.

The self-reinforced structure of the invention is also achieved

by combining the melt of an absorbable polymer and fibers, threads or similar reinforcement units of the same material, forming the mixture of the polymeric melt and the reinforcement units into the desired shape, and cooling the formed polymeric composite material so rapidly that the reinforcement unit does not significantly lose its internally oriented structure.

One can also produce the self-reinforced absorbable material in the invention by heating absorbable fibers, threads or similar structures in a pressed form under such circumstances that at least part of these structures partially softens or melts on the surface. Under pressure, the softened or melted surfaces of fibers, threads or similar structures are coalesced together, and when the casting cools, a self-reinforced composite structure is obtained. By carefully controlling the heating conditions, it is possible to process composite samples where the softened or melted surface areas of fibers, threads or similar units are very thin, and therefore the proportion of oriented fiber structure is very high, which leads to materials with high tensile strength, shear , bending and s 1 ag resistance values.

The above manufacturing principles can be used when the self-reinforced, absorbable materials are manufactured by batch processes (such as compression molding and transfer molding) or by continuous processes (such as injection molding or extrusion or pultrusion).

Typical properties of the materials in this invention are the high content of oriented fibers bound together with thin matrix polymer layers between the fibers, low porosity, smooth and compact surface, which properties are all achieved as a result of the application of pressure and possibly also heat during the production of the material. Good internal adhesion properties in connection with the above-mentioned advantageous structural factors give the material excellent mechanical strength properties such as high tensile strength, bending strength, compression strength or impact resistance.

It is of course that the self-reinforced absorbable surgical material, in addition to the matrix and reinforcing unit polymer, may if necessary contain additives such as dyes, powder-like fillers or other additives.

The self-reinforced materials in the invention can be used

in osteosynthesis implants such as surgical devices or as their components in the form of plates, pins, rivets, marrow rods, screws or in the form of other three-dimensional solids. The material can also at least form part of an osteosynthesis implant. It is natural that at least partially absorbable matrix and/or reinforcement units may contain such additives as colors, antioxidants, plasticizers, lubricants, fillers, etc., which are necessary in the treatment of the material or to modify its properties or the properties of the matrix and/or the amplification unit.

When the self-reinforcing material is used as a part

of a surgical plate, pin, rod, etc., the self-reinforced structure can form e.g. the core of the device and the surface of the device can be made from other materials. In this way, the excellent mechanical properties of the self-reinforced material can be combined with properties of other absorbable materials (such as slow absorption rate).

The self-reinforced material in the invention can also be used in several other ways in combination with other absorbable or other biostable materials. E.g. the mechanical properties of self-reinforced material can be modified by embedding absorbable reinforcement units with different hydrolytic properties than those of the self-reinforced material. Composites with excellent mechanical properties are also achieved when hybrid composites and self-reinforced materials with biostable fibers (such as carbon fibers) are produced.

De., the following non-limiting examples illustrate the present invention.

EXAMPLE 1

The melt of glycolide/lactide (90/10) copolymer (intrinsic viscosity |n| = 1.5 in 0.1% hexafluoroisopropanol solution (T = 25°C)) was mixed with the continuous fibers of the same material. The melt - fiber mixture was quickly formed into cylindrical samples (diameter 4.5 mm) which were quickly cooled, and whose fiber content was 30% by weight. The tensile strength of these self-reinforced absorbable composite rods was 260 MPa. The tensile strength of corresponding non-reinforced rods made from glycolide/lactide copolymer melt was 50 MPa.

EXAMPLE 2

Glycolide/lactide copolymer sutures ("Vicryl") (size

2 USP) was heated in vacuum at 185°C for 6 minutes, which caused partial melting of fiber elements of sutures. The material was compression molded into a cylindrical shape by pressure: on. 2000 bar, and it cooled quickly. The bending strength of these self-reinforced rods was 1.70 MPa. The flexural strength of corresponding unreinforced rods made from glycolide/lactide copolymers melt was 90 MPa.

EXAMPLE 3

Polyglycolide sutures ("Dexon") (size 2 USP) were heated in a cylindrical pressure mold (length 70 mm, diameter 4.5 mm) at 218°C for 5 minutes at a pressure of 2000 bar. The softened fiber material was partially fused and the cast was cooled rapidly to room temperature. The tensile strength of these self-reinforced absorbable composites was 380 MPa. The tensile strength of corresponding non-reinforced rods made from polyglycolide melt was 60 MPa.

EXAMPLE 4

Polyglycolide sutures ("Dexon") (size 2 USP) were melted at T = 230°C. The polymer melt and corresponding continuous sutures ("Dexon") were quickly mixed together, formed into cylindrical rods (diameter 3.2 mm) and rapidly cooled. The fiber content of self-reinforced rods was 40% by weight. Their tensile strength was 290 MPa. The tensile strength of corresponding non-reinforced rods made from polyglycolide melt was 60 MPa.

EXAMPLE 5

Isomers that can be used to produce absorbable osteosynthesis devices are e.g. isomers of polylactide such as poly-L-lactide (PLLA) and its DL isomer (meso lactide). PLLA is a crystalline polymer with a melting point of 180°C and the DL isomer is an amorphous polymer. The self-reinforced material can be produced from these materials by combining DL isomer matrix and PLLA fiber, wire or similar reinforcing unit structures to each other using heat and pressure.

Bundles of poly-L-lactide (PLLA) fibers (fiber diameter 12 ym, fiber amounts in a loosely twisted bundle = 200 pes, molecular weight of PLLA = 100,000) and the finely divided powdered DL isomer (meso lactide) (molecular weight = 100,000 ) were mechanically mixed and compression molded at 165°C and 2000 bar pressure for 6 minutes and rapidly cooled. The fiber content of self-reinforced rods was 50% and their tensile strength was 300 MPa. The tensile strength of unreinforced rods made from polymer melts was:

PLLA 60 MPa and mesolactide 55 MPa.

EXAMPLE 6

Self-reinforced rods from example 3 were coated in injection molding with a 0.2 mm thick layer of poly-p-dioxanone melt (J nI = 0.8 in 0.1% tetrachloroethane solution (T = 25°C) , Trø = 110°C) which gives cylindrical, coated self-reinforced rods with a diameter of 4.9 mm. The bending strength of the rods was 330 MPa.

After three weeks of hydrolysis in distilled water (T = 37°C), the coated self-reinforced rods had a flexural strength of 160 MPa, while the flexural strength of uncoated self-reinforced rods was 90 MPa.

EXAMPLE 7

Poly-L-lactide (Mw = 100,000) fibers (diameter 12 ym) were heated in a cylindrical press mold (length 70 mm, diameter 4.5 mm) at 180°C for 7 minutes at a pressure of 2000 bar. The softened fiber material was partially fused and the cast was cooled rapidly to room temperature. The tensile strength of these self-reinforced absorbable composite rods was 270 MPa. The tensile strength of corresponding non-reinforced rods produced from poly-L-lactide melt was 50 MPa.

EXAMPLE 8

Poly-B-hydroxybutyric acid (M = 80,000) fibers (diameter 15 ym) were heated in a cylindrical press mold (length 70 mm, diameter 4.5 mm) at 175°C for 5 minutes at a pressure of 2000 bar. The softened fiber material was partially fused and the cast was cooled rapidly to room temperature. The tensile strength of these self-reinforced absorbable composite rods was 200 MPa. The tensile strength of corresponding unreinforced rods made from poly-B-hydroxybutyric acid melt was 40 MPa.

EXAMPLE 9

Polydioxanone sutures (PDS by Ethicon) (size 0) were heated in a cylindrical pressure mold (length 70 mm, diameter 4.5 mm) at 10 3°C for 6 minutes with a pressure of 20 00 bar. The softened fiber material was partially fused and the cast was rapidly cooled to room temperature. The shear strength of these self-reinforced absorbable composite rods was 140 MPa. The shear rate of corresponding unreinforced rods made from polydioxanone melt was 50 MPa.

EXAMPLE 10

Polyesteramide (of the chemical formula VI, where R]_ = R2 = -(CH2)12~; Mw = 60,000) fibers (diameter 12 ym) were heated in a cylindrical press mold (length 70 mm, diameter 4.5 mm) at 105 C for 4 minutes with a pressure of 2000 bar. The softened fiber material was partially fused and the cast was rapidly cooled to room temperature. The shear strength of these self-reinforced absorbable composite rods was 140 MPa. The shear strength of corresponding non-reinforced rods made from polyesteramide melt was 50 MPa.

EXAMPLE 11

Polyglycolide ("Dexon") sutures (size 2) mixed with 10% by weight carbon fibers (6 µm in diameter) were heated in a cylindrical pressure mold (length 70 mm, diameter 4.5 mm) at 218°C for 5 minutes at a pressure of 2000 bar. The softened polyglycolide fiber material was partially fused, and the cast was rapidly cooled to room temperature. The tensile strength of this self-reinforced absorbable hybrid composite material containing carbon fibers was 450 MPa. The tensile strength of the corresponding carbon-

fiber reinforced material made from polyglycolide melt

- carbon fiber mixture was 160 MPa.

EXAMPLE 12

Glycolide/lactide copolymer sutures ("Vicryl") containing

10% by weight polyglycolide ("Dexon") sutures (size 2) were heated in vacuum at 185°C for 6 minutes, causing partial melting of the glycolide/lactide fiber units of the "Vicryl" sutures. The material was compression molded into a cylindrical mold (length 70 mm, diameter 4.5 mm) with a pressure of 2000 bar and it was rapidly cooled. A hybrid composite rod consisting of self-reinforced glycolide/lactide material with embedded polyglycolide sutures was obtained. The flexural strength of the hybrid composite material was 240 MPa. The flexural strength of the corresponding composition prepared from glycolide/lactide copolymer melt reinforced with 10% by weight polyglycolide sutures was 150 MPa.

EXAMPLE 13

Monofilament sutures (size 0) made from polyglycolide/trimethylene carbonate copolymer (Maxon from Davis + Geck) were produced in a cylindrical pressure mold (length 50 mm, diameter 3.2 mm) at 180°C for 8 minutes at a pressure of 2000 bar. The sutures were partially fused and the cast was cooled rapidly to room temperature. Self-reinforced absorbable rods with a shear strength of 110 MPa were obtained. The shear strength of similarly reinforced rods made from fully fused Maxon sutures was 60 MPa.

Claims (10)

1. Surgical osteosynthesizing agent or component of an osteosynthesizing agent with a composite structure such as a plate, a rod, a marrow nail or the like made of polymer or copolymer that is absorbable under tissue conditions, characterized in that the osteosynthesizing material or the component of the osteosynthesizing material has a self-reinforced structure, i.e. it consists of at least one matrix, which consists of absorbent polymer or copolymer and has as reinforcement absorbent fibers with a similar chemical structure. 2. Osteosynthesis material according to claim 1, characterized in that the reinforcement unit is in the form of fibres, threads, spirals, cords, ribbons, woven fabrics or the like. 3. Osteosynthesis material according to claim 1, characterized in that the absorbent matrix and the reinforcement units are produced from polyglycolide. 4. Osteosynthesis material according to claims 1 and 2, characterized in that the absorbent matrix and the reinforcement units are made of polyactide. 5. Osteosynthesis material according to claims 1 and 2, characterized in that the absorbent matrix and the reinforcement units are made of glycolide/lactide copolymer. 6. Osteosynthesis material according to claims 1 and 2, characterized in that the absorbent matrix and the reinforcement units are made of poly-P-hydroxybutyric acid. 7. Osteosynthesis material according to claims 1 and 2, characterized in that the absorbent matrix and the reinforcement units are made of polydioxanone. 8. Osteosynthesis material according to claims 1 and 2, characterized in that the absorbent, matrix and reinforcement units are made of polyesteramide. 9. Method for the production of an osteosynthesis material or a component according to each of the preceding claims, characterized in that the self-reinforced structure is provided by feeding into a melt of the absorbent polymer reinforcement fibers produced from corresponding materials, by shaping the resulting mixture of polymer melt and fibers into a desired shape and by cooling the shaped mixture of the polymer melt and the fibers so quickly that the fibers do not have time to melt significantly. 10. Method for producing an osteosynthesis material or a component according to each of the preceding claims 1-8, characterized in that the self-reinforced structure is provided by heating the absorbent fiber material so that the fiber material partially melts, whereby the melted material moistens remaining fibers, by shape the mixture of the fibers and the forge, e.g. in a mold or a nozzle, as well as by cooling the thus obtained composite structure into a product or semi-finished product.